An ink having a viscosity of 10 to some 100 centipoises described in Japanese Patent Laid-Open No. Hei 4-258677 has so far been reported as a water based ink using as a colorant titanium oxide, which is a white pigment. However, since this ink does not inhibit titanium oxide from settling, it has to be stirred again in use and has had the inconvenience that a ball for stirring has to be put in a tank for storing.
In contrast with the ink described above, as a water based white color pigment ink for a ballpoint pen which does not settle titanium oxide, an ink comprising a white pigment, tabular silicate and a water soluble resin and having a viscosity of 6,000 to 100,000 centipoises is reported in Japanese Patent Laid-Open No. Hei 6-287499. However, this ink has the problem that it has a high viscosity and is inferior in a follow-up property in writing.
Further, reported in Japanese Patent Laid-Open No. Hei 7-216283 is an ink comprising a white pigment and a nonionic surfactant having an HLB of 17.0 or more and having a viscosity of 6,000 to 50,000 centipoises. This ink also does not solve the problem that the follow-up property in writing is not good because of a high viscosity value.
Further, reported in Japanese Patent Laid-Open No. Hei 8-12916 is an ink comprising titanium oxide, a thickening water-soluble resin and a sugar alcohol and having a viscosity of 6,000 to 50,000 centipoises and a viscosity index of 2 or more which is obtained from a revolution difference of a viscometer. However, even if this viscosity index is met, the inferior follow-up property of the ink in writing quickly and splitting of the drawn lines are not solved. In addition thereto, only a white pigment is added as a coloring material, so that the ink has the problem that the marking performance is inferior on writing paper having a white ground.